Dear All,
I have attached a Sewer Cad file. My question was, Why the model cant have all positive pressure? I tried to increase the Head of pump but the system is still having negative pressure? What does it mean? How to rectify this?
Please Help!
Thanks & Regards,
June
Usually the reason you have negative pressures in a force main system is trying to pump over a high point. In that case, the high point acts as a siphon which may be all right if it is a small hill but if it is over 32 ft (9.8 m), it won't work. You should have an air valve at the top of any significant high point so that you don't build up a gas pocket at that point.
Answer Verified By: june_0809@yahoo.com
Sir Tom,
Is there any way that I can make it positive? Because for my client's side, they are asking why it turns out negative? why it doesnt show positive If it is working fine?
Next question was, what is the reason behind that 32ft(9.8m), that the system wont work?
Thank you very much!
Best Regards,
An air valve at the high point will eliminate the negative pressure.
Water vaporize when the pressure drops below -32 ft.
I tried to put air valve but it doesnt remove the negative (-) pressure.?
Is there any settings needed for the air valve?
Regards,
Make sure "treat as junction" is set to "false". Check the below technote on modeling air valves at high points:
communities.bentley.com/.../2644.modeling-force-mains-with-air-valves-tn.aspx
Jesse DringoliTechnical Support Manager, OpenFlowsBentley Communities Site AdministratorBentley Systems, Inc.